"The fans make that event," the golfer said Wednesday, per Todd Archer of ESPN. "The fans make that special. If we're not playing in front of fans, it's just like us playing a game in Florida."
While events earlier in the year have been canceled or postponed because of the coronavirus pandemic, the Ryder Cup is still scheduled to take place from Sept. 25 to 27 at Whistling Straits in Wisconsin.
However, PGA of America CEO Seth Waugh told Talkin' Golf With Ann Liguori (h/t Josh Berhow of Golf.com) in April that it might be necessary to hold the event without fans.
The PGA Tour is returning from a three-month hiatus this week for the Charles Schwab Challenge at Colonial Country Club, but it is closed to the general public.
Koepka, who has played in the last two Ryder Cups for Team USA, explained why fans are so important for the international event:
"If there's no fans out there you're not going to see guys fist pumping and that passion behind it. Yes, I love to play for my country, I love to do all these things, but it's important to have the fans there. We feed off it. The fans get louder or they'll boo you depending on what you're doing, but that's the beauty of it. The Ryder Cup is a true sporting event. It's different than any other golf tournament we play. It's a true sporting event, and I think if we can have fans, that's perfect, and if we can't, it just seems kind of like an exhibition, which it kind of already is. I just don't want to play it without fans."
The four-time major champion is not alone in his opinion.
"I think there's enough people within the game that don't want the Ryder Cup to happen without fans," Rory McIlroy said.
U.S. captain Steve Stricker previously said on the The Golf Affect Radio Show (via Bob Harig of ESPN) that the event without fans would be a "yawner." Jon Rahm told the Golf Channel "there's no point" in hosting the tournament without fans.
The strong opinions from representatives on both the United States and European teams could force the Ryder Cup to postpone to 2021 if fans are not able to attend.